1 Introduction
Lake eutrophication is a process in which excessive nutrients are accumulated in lakes, and it results from natural factors and human activities (Zou et al. 2020). Lake eutrophication leads to the massive growth and reproduction of algae in water column, thereby reducing the stability of water ecosystems, and thus it has posed a global environmental problem (Le Moal et al. 2019; David et al. 2020). At present, the prevention and control strategies against lake eutrophication mainly include physical, chemical, and biological ones. Specific technologies mainly include aeration, oxygenation, mechanical removal of phytoplankton, dredging, and sediment removal, the addition of flocculants and algaecides, phytoremediation (Schindler et al. 2008; Qin et al. 2013; Niemistö et al. 2020; Zhang et al. 2020). However, it is difficult to use physical and chemical methods for effectively solving the problem of lake eutrophication, in contrast, biological and ecological methods can continuously reduce pollutants in lakes, meanwhile maintaining the stability of the ecological environment.
Submerged macrophytes are the main primary producers in aquatic ecosystems and play an important role in maintaining biodiversity and water ecosystem stability (Malecki-Brown et al. 2010; Phillips et al. 2016). These plants can provide habitat for organisms, absorb nutrients from the water body and sediments, and control sediment suspension (Horppila and Nurminen, 2003; Veraart et al. 2011; Xian et al. 2022). Le Bagousse-Pinguet et al. (2012) found that interactions between submerged macrophytes can promote plant growth and reproduction in harsh environments, and also facilitate the growth of target macrophytes threatened by severe eutrophication. Submerged macrophytes are also very important for improving the eutrophication state of lakes (Gao et al. 2017).
The ability of submerged macrophytes to establish good roots in sediment is a key element for their growth. The physical and chemical properties of sediments play a very important role in the root growth of submerged macrophytes (Lin et al. 2020), and they affect the process of rooting, germinating, and stable growth of plants (Rattray et al. 1991; Xie et al. 2005). Submerged macrophytes can also absorb nutrients directly from the sediment to meet their own nutritional needs (Carr and Chambers. 1998). However, high contents of organic matter, nitrogen, phosphorus, and other nutrients in eutrophication sediments accelerates the eutrophication and water bloom (Qiu et al. 2016), thus limiting the growth and distribution of submerged plants (Soana et al. 2012; Zhu et al. 2016). Therefore, it is necessary to improve the sediment for the stable growth of submerged macrophytes.
Nutrients in sediments are readily released into the water under certain conditions (Peng et al. 2021). Addition of the substrates onto the sediment surface can inactivate sediments and slow the release of pollutants and nutrients from them into the water (Wang et al. 2019). The common sediment-modifying substrates have been widely used for ecological restoration due to their environmentally friendly nature (Larsen et al. 2004; Liu et al. 2021). Moreover, substrate not only affects the removal efficiency of pollutants from the water body by aquatic plants, but also affects the growth rate of plants (Zotina et al. 2014). Some studies have found that the substrate is the key factor to promote the growth of submerged macrophytes (Jones et al. 2012; Xu et al. 2016). However, there is still a lack of understanding of the links between the substrate and the growth state of submerged macrophytes or the sediment microenvironment.
Considering it, this study added four different kinds of commonly used substrates to the sediment and planted Vallisneria natans (Lour.) Hara (V. natans ). The aim of this study was to: (1) investigate the effects of different substrates on the growth and physiological and biochemical properties of V. natans , and (2) compare the effects of different substrates on microorganisms in rhizosphere sediments.